Dab2ip Regulates Neuronal Migration and Neurite Development
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DAB2IP REGULATES NEURONAL MIGRATION AND NEURITE DEVELOPMENT IN THE DEVELOPING NEOCORTEX by GUM HWA LEE A Dissertation submitted to the Graduate School-New Brunswick Rutgers, The State University of New Jersey And The Graduate School of Biomedical Sciences University of Medicine and Dentistry of New Jersey In partial fulfillment of the requirements For the degree of Doctor of Philosophy Graduate Program in Cell and Developmental Biology Written under the direction of Gabriella D’Arcangelo And approved by New Brunswick, New Jersey October, 2012 ABSTRACT OF THE DISSERTATION DAB2IP REGULATES NEURONAL MIGRATION AND NEURITE DEVELOPMENT IN THE DEVELOPING NEOCORTEX By GUM HWA LEE Dissertation Director: Gabriella D’Arcangelo Dab2ip (DOC-2/DAB2 interacting protein) is a member of the Ras GTPase- activating protein (GAP) family that has been previously shown to function as a tumor suppressor in several systems. Dab2ip is also highly expressed in the brain where it interacts with Dab1, a key mediator of the Reelin pathway that controls several aspects of brain development and function. I found that Dab2ip is highly expressed in the developing cerebral cortex, but that mutations in the Reelin signaling pathway do not affect its expression. To determine whether Dab2ip plays a role in brain development, I knocked down or over expressed it in neuronal progenitor cells of the embryonic mouse neocortex using the in utero electroporation technique. Dab2ip down-regulation severely disrupts neuronal migration, affecting preferentially late-born principal cortical neurons. Dab2ip overexpression also leads to migration defects. Structure-function experiments in ii vivo further show that both PH and GRD domains of Dab2ip are important for neuronal migration. A detailed analysis of transfected neurons reveals that Dab2ip down- or up- regulation disrupts the transition from a multipolar to a bipolar neuronal morphology in the intermediate zone. Knock down of Dab2ip in neurons ex-vivo indicates that this protein is necessary for proper neurite development and for the expression of several major neuronal microtubule associated proteins (MAPs), which are important for neurite growth and stabilization. To further investigate the role of Dab2ip in the developing brain, I also conducted Western blot analysis of brain lysates obtained from Dab2ip knockout mice. I found that Dab2ip deficiency results in the abnormal activity of signal transduction pathways involving the Erk1/2 and Akt kinases during early embryonic brain development, and confirmed that Dab2ip is necessary for the expression of MAPs. Furthermore, I discovered that Dab2ip is required for maintaining the normal levels of Dab1 specifically during embryonic, but not postnatal, brain development. Thus, this study identifies, for the first time, a critical role for Dab2ip in mammalian cortical development and begins to reveal molecular mechanisms that underlie this function. iii Acknowledgements First of all, I would like to express my deepest gratitude to my thesis advisor, Dr. Gabriella D’Arcangelo, for her guidance and support throughout my graduate study. Her patience and encouragement helped me stay motivated when I took on challenging thesis work. Her scientific expertise and enthusiasm have made her my role model and guided me to be a better scientist. I deeply appreciate her trust in me when I strived to balance lab works and taking care of my baby by myself as a weekly couple. Her endless support in my graduate life made me successfully complete my path to a Ph.D. degree. I would like to thank the committee members of my dissertation, Dr. Bonnie Firestein, Dr. Shu Chan Hsu, Dr. Mladen-Roko Rasin, and Dr. Karl Herrup. During all committee meetings, they have encouraged me and directed my thesis work to a logical path with tremendous discussions. The sincere guidance and willingness to share their experience and knowledge served as a strong base for developing my scientific attitude in a professional way. In addition, I would like to thank all members of D’Arcangelo lab. They have been always supportive and willing to help me with whatever I needed for the last five years. Specially, Dr. Odessa Yabut, now a post-doc in California, taught me lots of basic biochemical skills and in utero electroporation technique. Also, I thank her for her kindness as one of my best friends. Lastly, I cannot thank enough my lovely family for their support. Even though they are in Korea, my parents and parents-in-law always encouraged and helped me to focus on study and family. I thank my mother who is recovering from cancer but is still concerned about me, and my father who is incredibly considerate to me. I also appreciate my parents iv in law for being here to take care of Joshua for two months when he was born. I would like to thank my son, Joshua, who is now 3 years old and growing bigger everyday just like other children. I am so proud of him. Finally, I deeply thank my husband, Yunjong Lee. He is not only my lovely husband and a good father to Joshua, but also my scientific company who gave me a plenty of advice. Also, I am thankful for his efforts and sacrifice to be here every weekend to see me and Joshua for almost 3 years, due to the distance of schools that we attend. v Table of Contents ABSTRACT OF THE DISSERTATION ........................................................................... ii Acknowledgements ............................................................................................................ iv List of Tables ................................................................................................................... viii List of illustrations ............................................................................................................. ix Chapter 1. Introduction ....................................................................................................... 1 1. Development of neocortex ....................................................................................... 1 1-1. Generation of excitatory pyramidal neurons .................................................... 5 1-2. Radial migration of excitatory pyramidal neurons ........................................... 7 1-3. Generation and tangential migration of inhibitory interneurons .................... 17 2. Dab2ip .................................................................................................................... 19 2-1. Functions ............................................................................................................. 19 2-2. Expression ........................................................................................................... 20 2-3. Structural features ............................................................................................... 24 2-4. Genetic studies .................................................................................................... 25 Chapter 2. Dab2ip regulates neuronal migration and neurite development in the neocortex. ........................................................................................................................................... 27 1. Introduction ............................................................................................................ 27 2. Materials and Methods ........................................................................................... 28 3. Results .................................................................................................................... 35 vi 4. Discussion .............................................................................................................. 66 Chapter 3. Dab2ip controls the expression of Dab1 in the embryonic mouse brain; analysis of Dab2ip-knockout brain lysates. ...................................................................... 71 1. Introduction ............................................................................................................ 71 2. Materials and Methods ........................................................................................... 74 3. Results .................................................................................................................... 77 4. Discussion .............................................................................................................. 88 Chapter 4. Discussion and Future Directions ................................................................... 91 1. Dab2ip is required for radial neuronal migration. ................................................. 91 2. Rescue trials for the migration defect that is induced by Dab2ip RNAi ............... 94 3. Future Direction ..................................................................................................... 96 3-1. IUE with Dab2ip KO embryos to confirm the morphological phenotype. ........ 96 3-2. Potential effects of Dab2ip on the proliferation and differentiation of neural progenitors. ................................................................................................................. 96 3-3. The function of Dab2ip in dendritic spine development. ................................... 98 Bibliography ................................................................................................................... 105 vii List of Tables Table 1. Information of the primary antibodies applied in this study. ............................. 32 Table 2. Information of the secondary antibodies applied in this study.